The present invention relates to safe doors and walls, and more particularly to a protective filling for such doors and walls against cutting therethrough by an oxidizing flame cutting torch, on the one hand, and by mechanical cutting operations such as drilling or sawing, on the other hand (hereinafter called for short "T & D Protection").
T & D protected safe doors and walls are presently made of a series of steel plates interposed between a series of ferrous or non-ferrous metal plates; the latter plates, which are known to possess high heat conductivity rates provide the necessary resistance against flame cutting, whereas the former, against drilling, hammering, sawing and the like mechanical cutting methods.
Such modular or hybride structure doors and walls are costly in production and difficult in the handling and assembling thereof.
Over sixty years ago, it was for the first time proposed to achieve T & D protection of vault doors by forming the doors with a core of a drill-proof material and casting therearound a sheath of heat-conductive metal. (Guardian Metals Co. U.S. Pat. Nos. 1,755,913 and 1,815,187).
According to the last mentioned patent, there have been prepared safe and vault members comprising a cast-metal matrix of high heat conductivity in which there were embedded a plurality of slabs of metallic material in substantial parallelism, such slabs being tool-resistant and being made up of a composition consisting of 13-20% manganese, 13-18% chromium, 2-4% carbon and the balance iron.
As exemplified in the specification, the composite slab assemblies were made up of slats so arranged as to provide overlapping between the several slats, thus preventing the formation of any direct apertures from one side to the other. These members were set in position in a suitable mold, spaced apart a suitable distance, and a sheath of heat resistant metal was cast therearound.
The slat members were cast up in the usual manner, and were provided with inserts in the form of a mesh of malleable iron rods or wire for reinforcing the cast slats, particularly where large dimension slats were used.
This T & D protection method never gained commercial success, due to the following main reasons. Since the outer casting or sheathing was inherently soft and weak, it was quite easily possible to drill or otherwise cut through the cast material (e.g. with a compass-saw) precisely around an embedded slab, thus attaining access thereto. The entire slab could then be pulled out, and the procedure be repeated with respect to the following, deeper embedded slab, until an opening in the door was formed.
Furthermore, rather than attempting to withdraw a complete slab, it had frequently happened that, again, a portion of the soft sheath was mechanically removed, and the opening continued through the cast iron or steel slab by a torch, and so forth. In fact, after reaching and melting part of the first slab, the proceeding process of flame-cutting--even through the supposedly torch-proof material--became less difficult because the molten metal of the slab actually catalyzed the fusion of the surrounding metal.
It will also be noted that the inner spaced occupied by the relatively large slabs, seriously affected the heat conductivity properties of the wall as a whole.